2 Cell Division Meiosis Abnormal Meiosis nondisjunction occurs when two homologous chromosomes fail to separate during meiosis or mitosis.one of the daughter cells will have too many chromosomes, while another will have too few.the effects of nondisjunction are more devastating in the production of gametes.nondisjunction occurs during anaphase I or anaphase II
3 Cell Division Meiosis nondisjunction in humans produces: gametes with 22 and 24 chromosomes.if the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced.the zygote will have three chromosomes rather than a pair.this condition is referred to as trisomy.
4 Cell Division Meiosisif the gamete with 22 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 45 chromosomes is produced.the zygote will have one chromosome rather than a pairthis condition is referred to as monosomy.once the cells of trisomic or monosomic zygotes begin to divide, each cell of body will be one plus or one minus a chromosome.
6 Cell Division Meiosis Nondisjunction Disorders Male and Female SyndromesDown Syndrometrisomy 21Patau Syndrometrisomy 13Edward Syndrometrisomy 18E) Abnormal Meiosis
7 Down’s Syndrome cause: trisomy of the 21st chromosome symptoms: mental retardation,a round full face, enlarged tongue, large foreheadshort statureshortened lifespanhigher risk of other medical conditions, such as heart defects(50%), leukemia(10-50 times more common), Alzheimer’s, etcprevalence:the most common non-lethal non-disjunction disorderaffects about 1 in 800 babies (risk increases significantly with age of mother)Reporduction is also affected. Only 3 recorded instances of DS males fathering children. Cataracts and glaucoma are very commmon. Abortion rates are high (92%). Some people have resorted to cosmetic surgery to reduce the appearance of DS to improve quality of life but it is very controversial.
8 Patau Syndrome cause: trisomy of the 13th chromosome symptoms: least common and most severe of the autosomal trisomiessymptoms:extreme facial deformation (e.g. cyclopia, missing nose)polydactylylong term neurological disability,heart defects, frequent pneumonia and other respiratory infections.prevalence: about 1 in 10,000 live birthsprognosis:very poor, most embryos do not survive gestation and are spontaneously abortedof those surviving to term gestation, approximately 82-85% do not survive past 1 month of age, and 85-90% do not survive past 1 year of age (there have only been 5 cases reported in the medical history of patients living beyond 10 years of age)
9 Edwards Syndrome cause: trisomy of the 18th chromosome symptoms: low birth weight;a small, abnormally shaped head; small jaw; small mouth; low-set ears;clenched fists with overlapping fingers.breathing or heart defects normally associated with premature babiesprevalence:1:3000 live birthssecond most common autosomal trisomyincreased risk as a woman's age increasesprognosis:very poor - about half die in uteroof liveborn infants, only 50% live to 2 months, and only % will survive their first year of life. Median life span is 5-15 days.medical interventions for related medical problems (e.g. heart defects) usually withheld due to poor prognosis
11 Turner’s Syndromecause: sex chromosomes undergo non-disjunction, causes a monosomic femalefemale only has one X chromosome instead of the normal twoit is the only known viable monosomy in humansdoes not occur in males because the embryo cannot survive without at least one X chromosome(females born as XXX are healthy and cannot be distinguished from normal XX females except by karyotype)symptoms: (females only)sexually underdeveloped,tend to be short and have thick, widened neckssterility, congenital heart disease and hypothyroidismprevalence:1 in 5,000 birthsmost Turner’s embryos resulting in miscarriages
12 Klinefelter Syndromecause: again, a non-disjunction of the sex chromosomes, but this time producing a trisomyat birth, the child will have primary male sex characteristics and will appear maleat puberty, he will begin producing high levels of female sex hormones (e.g. estrogen)(males with an extra Y chromosome used to be thought of as destined to be criminals; now we know them typically to be only taller than average)symptoms: (males)though he has male sex organs, they are small and the man is sterilehe will have breast enlargement and other female body characteristicsX-linked recessive conditions occur less frequently than in normal malesprevalence: 1 in 1000 births
13 Cell Division Meiosisthe chances of nondisjunction disorder increases with agechances of having a child with Down’s Syndromeconceiving between 20 and 24 years, 1 in 1490conceiving at age 40, 1 in 106conceiving at age 49, 1 in 11E) Abnormal Meiosis
16 Cell Division Meiosis- Recall Karyotypea chart of chromosomes.obtained by mixing a small sample of tissue with a chemical that stimulates mitotic division.division is the stopped during metaphase.chromosomes are staineda picture is taken and chromosomes are paired up with their homologue.homologue chromosomes are similar in size, length, centromere location and banding pattern.they are organized in decreasing size with the sex chromosome placed at the end.